The present invention relates to food containers and methods and apparatus for making food containers, and more particularly relates to methods of sealing such containers.
Food and drink products and other perishable items are often packaged in tubular containers, which are sealed at both ends. These tubular containers typically include at least one structural body ply and are formed by wrapping a continuous strip of body ply material around a mandrel of a desired shape to create a tubular structure. The body ply strip may be spirally wound around the mandrel or passed through a series of forming elements so as to be wrapped in a convolute shape around the mandrel. At the downstream end of the mandrel, the tube is cut into discrete lengths and is then fitted with end closures to form the container.
Tubular containers of this type typically include a liner ply on the inner surface of the paperboard body ply. The liner ply prevents liquids, such as juice, from leaking out of the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the liner ply is also resistant to the passage of gasses, such as oxygen and nitrogen, so as to prevent odors of the food product in the container from escaping and to prevent atmospheric air from entering the container and spoiling the food product. Thus, the liner ply provides barrier properties and the body ply provides structural properties.
In addition, current commercial containers often have membrane-type lids or end closures heat sealed to a curled or bead-shaped rim of the composite container wall to form a peelable seal. The rim is formed by turning outwardly the end of the container to position the inner layer of the liner material on the outwardly curved surface. The membrane-type lid is sealed to the liner on the rim by way of a heat sealable composition disposed on one or both of the membrane-type lid and the liner.
During construction of a sealed container of the type described above, a tacky paraffin wax is conventionally applied to the container rim in order to hold the lid in place prior to heat sealing. The wax interferes with the seal strength of the seal created between the membrane lid and the container. The lowered seal strength can result in poor high temperature and altitude performance and greater likelihood of seal failure. Vacuum-based systems that draw a vacuum within the container to hold the lid in place prior to heat sealing have been used as an alternative to the application of wax. However, such systems add equipment cost and complexity to the process. As a result, there remains a need in the art for a method of holding the lid in place prior to heat sealing without specialized equipment or adversely affecting the strength of the heat seal.
The present invention eliminates the use of conventional wax and vacuum machines, and advantageously provides a tacky composition that is compatible with the heat sealable composition used to create the heat seal between the liner of the container and the lid. The tacky composition of the present invention does not interfere with the seal strength of the heat seal and allows formation of a fusion seal between the lid and the container. The appropriate tacky composition is selected based on the type of material used to form the heat seal.
The present invention provides a sealed composite container comprising a tubular body member having at least one paperboard body ply and a liner ply adhered to the inner surface of the tubular body member. The liner ply comprises a barrier layer. At least one end of the body member and the liner ply are rolled outwardly to form a rim and expose the liner ply. A lid is positioned against the rim, the lid comprising a barrier layer. A tacky composition is in contact with both the rim and the lid and is operatively positioned therebetween. The tacky composition has sufficient tackiness to temporarily hold the lid in place overlying the rim prior to heat sealing. At least one of the lid and the liner ply further comprises a seal layer comprising a heat sealable composition. The tacky composition and the heat sealable composition form a heat seal between the lid and the liner ply. The tacky composition is chemically compatible with the heat sealable composition such that the two compositions are fusion sealed together.
In one embodiment, the tacky composition and the heat sealable composition both comprise a polymer material having a non-polar polymer backbone with at least one polar functional group connected thereto. For instance, the polar functional group may comprise carboxylic acid and the polymer backbone may comprise polyethylene. Preferably, the tacky composition has a melt flow index of about 20 g./10 min. to about 2000 g./10 min. Advantageously, the tacky composition is selected from a group consisting of ethylene/acrylic acid waxes, ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, polyvinyl alcohol and mixtures thereof. Preferably, the seal layer is selected from the group consisting of high density polyethylene, low density polyethylene, ethylene vinyl acetate, ethylene methyl acrylate, metallocene catalyzed polyolefins and mixtures thereof.
The present invention also provides a method of manufacturing a sealed container. The method includes providing a tubular member having at least one paperboard body ply and a liner ply adhered to the inner surface of the body ply. At least one end of the tubular member is rolled outwardly to form a rim. A lid is provided for closing the end of the tubular member, the lid comprising a barrier layer. Additionally, at least one of the lid and the liner ply further comprise a seal layer comprising a heat sealable composition, the seal layer being operatively positioned to form a heat seal between the lid and the liner ply. A tacky composition is applied to the rim and the rim and lid are contacted such that the tacky composition is positioned therebetween. In this manner, the tacky composition temporarily affixes the lid to the rim. The seal layer is heated under conditions sufficient to render the heat sealable composition of the seal layer flowable. The rim and lid are pressed together to form a heat seal therebetween, wherein the heat seal comprises the tacky composition and the heat sealable composition. Since the tacky composition is chemically compatible with the heat sealable composition, the two compositions are fusion sealed together, thereby hermetically sealing the lid to the liner ply.
The tacky composition may be applied by coating at least a portion of the outer surface of an applicator with the tacky composition and contacting the coated portion of the applicator with the rim of the container such that an amount of the tacky composition is applied to the rim. The applicator is preferably selected from the group consisting of brushes, rollers, and sponges.